Equivalent circuit analysis of harmonic distortions in photodiode

We report a simple method to obtain a p-i-n photodiode's harmonic distortion levels at different frequencies from the microwave reflection coefficient S/sub 11/ of the photodiode under dc illumination. This approach is based upon the tracking of the photodiode's microwave impedance with S/sub 11/ at different incident optical powers before severe saturation occurs at low bias or at high optical power. The second-harmonic distortions measured from a waveguide photodiode agree closely with those predicted from the S/sub 11/ data.